1. Field of the Invention
The present invention relates generally to semiconductor devices and particularly to semiconductor devices including a high breakdown voltage device employed in a drive control circuit for operating induction motors and the like.
2. Description of the Background Art
To operate an induction motor or a similar load a drive control circuit (a driver circuit) is provided. The driver circuit includes a first driver circuit responsible for an operation delivering a current to the load (an operation A) and a second driver circuit responsible for an operation drawing a current from the load (an operation B) and operations A and B are alternately performed. To alternately perform operations A and B, the first and second driver circuits have a first IGBT and a second IGBT, respectively, alternately turned on/off. The first and second IGBTs are connected in series and a node connecting them is connected to the load.
In the first driver circuit the first IGBT has its gate turned on/off with reference to the node's potential to provide a switching operation between a high voltage potential and the node's reference potential. In the second driver circuit the second IGBT has its gate turned on/off with reference to a ground potential to provide a switching operation between the node's reference potential and the ground potential.
As the ground potential is fixed, using the ground potential as a reference to generate a pulse potential for turning on/off the gate of the second IGBT is not accompanied by a serious problem. If the node's potential is used as a reference, however, it will vary between the high voltage potential and the ground potential. Thus the node's potential varies in too large a range to generate a pulse potential for turning on/off the gate of the first IGBT.
Accordingly a semiconductor device (or circuit) including a field effect transistor and a predetermined resistor is provided. In this semiconductor device a range for which if the field effect transistor's drain voltage significantly varies its drain current substantially does not vary, i.e., a saturation range, is utilized to generate a fixed potential difference across the resistor to generate a pulse potential for turning on/off the gate of the first IGBT. One such drive control circuit is disclosed for example in Japanese Patent Laying-open No. 2001-145370.
However, conventional semiconductor devices have the following problem: If a semiconductor device is reduced in footprint to miniaturize the drive control circuit, a relationship with a depletion layer's extension occasionally makes it difficult to ensure sufficient breakdown voltage. Furthermore, if the semiconductor device is configured of semiconductor regions including a semiconductor region having some impurity concentration, it cannot ensure sufficient breakdown voltage.